Currently steel mills use large amounts of scrap steel obtained from various sources. The steel is purchased by grade and the price of the various grades of steel varies widely. The grades include briquettes, turnings, borings, municipal scrap, tire wire, tin can, tin plate, #2 bundles, #2 heavy melt, #1 heavy melt, plate and structural, shredded, busheling, #1 bundles, hot briquetted iron, direct reduced iron, pig iron, iron carbide, blast furnace iron reclaims, steel pot reclaims and steel mill home scrap. Other grades exist and within the grades the composition of the scrap may vary. The highest grade of steel scrap may be three times the cost of the lowest grade of scrap. Mills attempt to obtain batches of steel, known as a heat or a melt, by mixing these various grades to obtain the proper chemical composition and physical properties of the final product as well as to control processing variables such as yield, oxygen consumption and power consumption.
Steel mill operators currently rely upon visual inspection and the experience of the metallurgist to determine the composition of scrap fed into the melter of a steel mill. Based upon experience it is possible to roughly control the composition of the resulting melt. When using prior art methods of batch calculation it may be necessary to add lime, oxygen or high grade steel to bring a batch into conformance with a specification. At times it is not possible to bring a batch within the specification and the steel must then be diverted to another use. Typical mills operate with batch sizes ranging from 5-200 tonnes with annual melt capacity ranging up to 3 million tonnes. With this high throughput, even small errors in scrap selection may have substantial impact on the operating cost of the mill.
Bulk material analyzers are used to measure the elemental content of materials such as concrete used for construction purposes and coal for use in power generation. In bulk material analyzers, the material is transported through the material analyzer on a conveyor belt between at least one radiation source and at least one radiation detector. Typically, the radiation source includes a neutron source and the radiation detector includes one or more gamma-ray detectors. As neutrons bombard a material, characteristic quanta of energy are generated by stimulated emission. Stimulated emission is caused by the transfer of energy from the neutrons striking the atoms of the bulk material. The transferred energy drives the electrons of the material into an excited state and when the excited electrons revert to their base state quanta of energy, typically in the form of gamma-rays, are emitted. By analyzing the gamma spectra produced, the presence of different elements in the material may be measured. Based upon the relative intensities of the spectra, the ratio of the various elemental constituents may be ascertained. This measurement process is known as prompt gamma-ray neutron activation analysis (PGNAA).
Bulk material analyzers typically transport the material through the assembly on a conveyor belt or may drop the material through a chute. The conveyor runs between the radiation sources and the radiation detectors. Substantial shielding is included in the analyzer to prevent the escape of the neutrons and gamma-rays which are hazardous. The radiation detectors include scintilators which convert the gamma rays to light and photo-multiplier tubes which convert the light into electric signals which are sorted by their energy to generate gamma-spectra. A computer then analyzes the gamma-spectra to obtain the relative amount of each element in the sample.
Various bulk material analyzers, such as that disclosed by U.S. Pat. No. 4,582,992, "Self Contained, On-Line Real Time Bulk Material Analyzer" Inventor Atwell et al. (herein incorporated in its entirety by reference) and U.S. Pat. No. 5,396,071, "Modularized Assembly For Bulk Material Analyzer" Inventor Atwell et al. (herein incorporated in its entirety by reference) are known. U.S. Pat. No. 5,396,071, discloses a bulk material analyzer made up of individual modules that easily can be handled separately. Previously, the use of Bulk Material Analyzers has been limited to the measurement of sulfur and ash in coal fired electric plants and in cement plants to provide a consistent kiln feed.
Motion compensated scales have previously been used onboard ships to compensate for the movement caused by the pitch and roll of waves. A motion compensated scale typically includes one or more accelerometer and a computer which compares the output of the scale and the accelerometer to determine the actual weight of the object. One such motion compensated scale is set forth in U.S. Pat. No. 4,750,574, entitled "Accurate Weight Determination at Sea" inventor Williams (herein incorporated by reference in its entirety).
It has been known, at least in the area of stainless steels, to mix batches based upon the predetermined composition of scrap. Previously, the scrap composition was determined by standard sampling and spectrographic techniques.